The invention relates to a device for determining the position of a vehicle, comprising a GPS (Global Positioning System) receiver which supplies at regular intervals position data of the vehicle on the basis of data received from satellites, and also comprising a device for performing dead-reckoning on the basis of the position data from the GPS receiver, a compass and at least one wheel sensor, and a correction unit which corrects the dead-reckoning values, supplied at regular intervals by the dead-reckoning device, in dependence on comparisons with road or rail position coordinates read from a mass memory, notably with characteristic road or rail position coordinates, which correction unit outputs said corrected values as vehicle position coordinates.
In known devices of this kind, the current vehicle position is continuously determined by dead-reckoning, utilizing notably a compass and one or more wheel sensors. The errors then occurring can be corrected by comparison with road position coordinates read from a mass memory (map matching). Notably characteristic road position coordinates, for example curves in roads or intersections, can be readily recognized and the vehicle position determined by dead-reckoning can be corrected in conformity with the coordinates of the known, characteristic points.
This combination of dead-reckoning and correction by road position coordinates fails when the vehicle is started or, generally speaking, when the road position coordinates are unknown like after transport of the vehicle by rail or ship or the like. To this end, in known devices there is provided a GPS receiver which receives signals from GPS satellites and which is capable of calculating the position of the GPS receiver or the vehicle on the basis of the reception of said signals, notably on the basis of the phase shifts of these signals relative to one another. However, the accuracy of such position determination by means of a GPS receiver amounts to only a few hundred meters; this is inadequate, for example for accurate determination of the position of a vehicle in a city.
In known devices of this kind, the correction of the position data supplied by the GPS receiver is performed by means of a data channel. Via this data channel, the GPS receiver is informed from outside about the continuously varying magnitude and direction of the error, via an additional infrastructure to be provided.